Methods to further purify CDP reductase from both the epidermal and the dermal compartment of skin are being developed. Studies of the kinetics of ribonucleotide reduction in epidermis and dermis are being carried out. An isotope dilution procedure to measure nucleotide pools in epidermis and dermis is being used. The contribution of de novo pathways and salvage pathways for purine and pyrimidine biosynthesis in skin is being measured.